How fast is too fast?

A 46-year-old Santa Rosa woman seriously injured when her pickup was hit by a speeding CHP cruiser is suing the state, claiming the officer acted negligently in driving 104 mph in response to a report of teens with baggy clothing gathering outside the DMV.

Cynthia Dempsey will ask jurors next month to award her damages for the Highway 12 crash involving Officer Blair Hardcastle that left her with memory loss, facial scarring and post-traumatic stress disorder, said her lawyer, Brendan Kunkle.

"We don't think there was danger to person or property justifying an emergency response," Kunkle said. "Even if there was, the officer is required to be aware of others on the road and drive reasonably and safely for the circumstances. We don't believe he did so."

A CHP spokeswoman, Fran Clader in Sacramento, declined to comment on the case, citing a policy against discussing lawsuits. A CHP representative said Hardcastle would not comment because of the litigation.

Generally, officers are exempt from the rules of the road in pursuing criminal suspects or responding to emergencies. But they are still obligated to drive with the safety of others in mind, said Officer Jon Sloat, spokesman for the CHP in Sonoma County.

Sloat said the policy spelled out in the vehicle code lets the officer decide the level of urgency based on the circumstances.

"It's up to the officer how he thinks he needs to respond," Sloat said.

The crash happened on a Saturday evening, Sept. 26, 2009, just east of Highway 101 near the Sonoma County Fairgrounds.

Hardcastle, 24 at the time, is the son of Superior Court Judge Allan Hardcastle. He was stopped on Farmers Lane near the westbound entrance to Highway 12 with a ride-along passenger, Explorer scout Erik Epting, 19, of Windsor.

At about 6:30 p.m., he received a call that would send him down the freeway at more than 100 mph.

Dispatchers told Hardcastle that 25 to 30 teenagers had gathered in the DMV parking lot about 3 miles away and that the reporting party had "seen a lot of baggy clothing," Kunkle said.

It was later determined to be a group of middle school students practicing for a dance event, Kunkle said.

Acting on the information at the time, Hardcastle took off with overhead lights on and siren blaring, reaching a top speed of 104 mph near the fairgrounds, Kunkle said.

Ahead, Hardcastle and Epting saw a motorcycle get on the freeway at Maple Avenue and move into the fast lane in front of the patrol car.

Rather than braking, Hardcastle steered onto the median and passed the motorcycle on the left, Kunkle said.

He drove along the median until it abruptly ended, forcing him back onto the roadway. His car careened across two lanes and hit the back of Dempsey's truck in the slow lane, Kunkle said.

The impact flipped Dempsey's truck onto its roof and sent it skidding about 100 feet, Kunkle said.

Dempsey, a single mother who had been returning home after picking up a friend's dog, suffered a concussion, cuts on her eyelids and a partially severed ear, Kunkle said.

The dog lost its tail, he said.

She was taken to Santa Rosa Memorial Hospital, where she spent two days in recovery, he said.